Commemorating the 50th anniversary of the March on Washington, civil-rights leaders and elected officials gathered the site of the original event to decry voter-ID laws, the Supreme Court's recent decision on the Voting Rights Act, "Stand Your Ground" gun laws, and racial profiling.

Wednesday will mark a half century since Martin Luther King Jr. delivered the iconic "I Have a Dream" speech on Aug. 28, 1963. A rally is planned on the National Mall for the anniversary, and President Obama is scheduled to speak on the steps of the Lincoln Memorial.

But today, leaders convened at the Lincoln Memorial for the National Action to Realize the Dream March, which includes a morning prayer, a series of speeches and a march to the Washington Monument, past the Martin Luther King Jr. memorial, which was recently reopened after a paraphrased quote that had drawn criticism of the statue was sandblasted off.

"Trayvon Martin was my son, but he's not just my son, he's all of our son, and we have to fight for our children," said Sybrina Fulton, the mother of slain Florida teenager.

Martin's death in 2012 sparked national outrage and a broader discussion of gun laws and racial profiling, although race was not an issue in the trial of Martin's killer, George Zimmerman, who was found not guilty of murder. Zimmerman said he shot and killed Martin in self-defense.

Fulton was joined onstage by a cousin of Emmett Till, the Chicago teenager slain in Mississippi in 1955 after allegedly flirting with a white girl. Many attendees carried yellow signs reading, "Support Trayvon's Law," supporting changes to laws like Florida's "Stand Your Ground" law, even though that was not the basis of Zimmerman's defense.

"Fifty years later, their march is now our march, and it must go on," Holder told the crowd, pointing to a broadened push for equality for women, Latinos, Asian Americans, gays and lesbians, and people with disabilities.

Holder called on Americans to remember not just King, but all activists who staged sit-ins at lunch counters and faced fire hoses and police dogs in the civil-rights demonstrations of the 1960s.

"But for them, I would not be attorney general of the United States, and Barack Obama would not be president of the United States of America," Holder said.

Lewis, who led the Student Nonviolent Coordinating Committee (SNCC) spoke at the March on Washington in 1963 and was one of its organizers. He returned to the steps of the Lincoln Memorial today.

"Fifty years ago, I stood right here in this spot, 23 years old, had all of my hair and a few pounds lighter. So I've come back here again to say that those days, for the most part, are gone, but we have another fight," Lewis said. "We must stand up and fight the good fight as we march today, for there are forces, there are people who want to take us back."

Lewis pointed to the Supreme Court's decision this summer to strike a major provision of the Voting Rights Act, which has mandated that voting districts with histories of racial discrimination must seek federal approval for changes in voting policy. In June, the Court struck down the provision that determines which districts must undergo that federal scrutiny.

The 1965 Voting Rights Act was a landmark achievement of the civil-rights movement, which sought to enfranchise black Americans suppressed from voting in the South. Signed by president Lyndon Johnson, it followed the 1964 Civil Rights Act.

"I am not going to stand by and let the Supreme Court take the right to vote away from us," Lewis said. "The vote is precious. It is almost sacred. It is the most powerful nonviolent tool we have in a Democratic society, and we've got to use it."

In a National Urban League summit on Friday, the Supreme Court's decision -- along with "Stand Your Ground" gun laws, racial profiling, and income disparity -- figured prominently in activists' case for a continued push for racial equality. The Voting Rights Act decision was a theme again today.

"As we march today, we march with a determination to let you know that we don't have amnesia, we did not forget the price that's paid," Sharpton said, during the rally's keynote speech, blasting the Court's ruling.

"Old things have passed away. We see a new America," Sharpton said. "We march because we're going to bring a new America, one nation under God, indivisible, with liberty and justice -- not for some, not for who you choose, not for who you like, but for all."

Booker recounted his father telling him never to take his current place for granted, and to remember the struggles of civil rights activists before his time.

"I call on my generation to understand that we can never pay back the struggle and the sacrifices of the generation before, but it is our moral obligation to pay it forward," Booker said.

Martin Luther King III, the son of Dr. Martin Luther King, Jr., also pointed to the Supreme Court's decision, along with income disparity.

"Not only must we not be satisfied, we must fight back boldly," King said. "We know that the dream is far from being realized."

Joyce Batipps, who came out to be part of the commenmoration today, was 17 years old and just getting ready to start college at Howard University when she saw King speak in 1963.

"I stayed for the whole march, just dangling my feet in the reflecting pool," Batipps told ABC News. "Its thrilling to see that we made some change but we still have lots of support for more change."

Yvonne Johnson said she was 22 when she met King at the March on Washington.

"It was like magic. It was very important he was a very good speaker," Johnson said. "I think during Dr. King's time, people had a lot of respect for people of all colors -- it doesn't matter what color you were, he brought people together."

Events leading up to Wednesday's anniversary began in Washington, D.C., on Friday, with a two-day summit hosted by the National Urban League at the Grand Hyatt downtown.

With some help from Trayvon Martin's family, civil rights leaders and African-American politicians called for action, blasting voter-ID and "Stand Your Ground" laws in a ballroom in the hotel's basement.

"The dream is not a static dream, the dream lives and evolves," the Rev. Jesse Jackson Sr. told the crowd on Friday. "The dream of '63 was to end barbarism and humiliation. From Texas across to Florida, up to Maryland, we couldn't use a single public toilet."

Speakers repeatedly criticized "Stand Your Ground," stop-and-frisk and voter-ID laws. The NAACP's Benjamin Jealous blasted New York Mayor Michael Bloomberg, who instituted a stop-and-frisk policy. Waters offered a scathing critique of the Supreme Court and its "slick, calculated, dastardly decision to keep us from voting," referring to its June decision on the Voting Rights Act.

"Just like this [anniversary] is historic, we want to make our tragic incident historic for all people by letting the world, by letting the country know that we will continue to stand as parents, not only for our kids, but for all of our kids, and fighting for justice for all of our kids," Tracy Martin said.